1. Field of the Invention
The present invention relates to an optical recording method and apparatus for recording information on an optical recording medium by utilizing a laser beam.
2. Description of the Prior Art
According to the recording method of a conventional optical recording method, recording is performed by irradiating a laser beam on an optical recording medium to induce local temperature elevation or chemical change of the laser beam irradiated area by light absorption. For reproducing, a laser beam having a differnt intensity or wavelength from that used in recording is irradiated on the optical recording medium to detect the local change on the optical recording medium induced by recording from the change in reflected light or transmitted from the optical recording medium.
To describe in detail the recording method on a magneto-optical recording medium out of the optical recording media, recording is performed thermomagnetically by inducing local temperature elevation on a magneto-optical recording medium by irradiation with laser beam, and reproduction is performed by detecting the direction of magnetization in the recorded area by irradiating a weak laser beam having a linear polarization state by utilizing a Kerr effect or Faraday effect (i.e., magneto-optical effect) arrangement.
Furthermore, the recording systems include the following two systems: one being a system to perform recording by modulating the recording laser beam intensity in accordance with the recording signal under a certain recording magnetic field (in the case of an optical recording medium other than the magneto-optical recording medium, the recording magnetic field is unnecessary) (referred to as an optical modulation recording system), and the other being a system to be used for the magneto-optical recording medium only, for performing recording by modulating the direction of the recording magnetic field according to the recording signal under a certain recording laser beam intensity (referred to as a magnetic field modulation recording system).
In the conventional optical modulation recording system and the conventional magnetic field modulation recording system, when a high frequency recording signal is recorded, the shape of the recorded domain becomes as shown in FIGS. 7 and 8, respectively. More specifically, in the optical modulation recording system, the area of each recorded domain is smaller than the area of the reproducing laser beam spot as shown in FIG. 7, so that the amplitude of the reproduction signal is not adequately large, or the S/N ratio of the reproduced signal is low. In the magnetic field modulation recording system, each recorded domain has horn-like extended portions as shown in FIG. 8 which can be undesirably detected when the reproducing laser beam spot is positioned at an area between recorded domains. This reduces the S/N ratio of the reproduced signal and causes unwanted jitter in the reproduced signal.